Low-distortion Audio-range Oscillator - Page 23 - diyAudio
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Old 13th August 2012, 12:17 AM   #221
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Yes, interesting. I suspect the harmonic content there is coming from the mute, rather than the trumpet; that the trumpet is energising a secondary re-radiation from some active element in the mute. Being outside the horn, it's not limited by the normal horn roll-off. I looked up the Harmon mute:

"The Wah-wah mute (also known by the brand name Harmon) is a hollow, bulbous mute in two parts. Unlike the more common straight or cup mutes, the Harmon mute has a solid ring of cork that completely blocks all of the air leaving the bell, and forces all of the instrument's air column into the mute. In a hole on the front of the mute, there is a cup on a tube that can be slid in or out, or removed completely, depending on the composer's direction or the player's preference. The mute produces a sound perhaps best described as a highish-pitched 'buzz'. Harmon mutes are available for many brass instruments, but are only commonly used by trumpets and trombones."

Sounds more like a Kazoo than a mute! Indeed, is it fair use of the English language to call something that brightens the tone a "mute"?!

Even so, the levels around 20kHz are still about 40dB down, so my concerns remain - are we likely to get intermod products of enough energy to be audible, especially in the presence of the complex original sound?

I guess, though, the elegant simplicity of testing at the middle and the extremes as Bob recommends is that you then don't have to worry about these sorts of things! Teetering...

Terry
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Old 15th August 2012, 05:43 AM   #222
1audio is offline 1audio  United States
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I got Victor's (vicnic) oscillators today. He has done a marvelous job and I'm quite happy with them and would recommend them to anyone who need a low distortion source.

I'm waiting for the remaining batteries from China to finish the assembly.

A quick test on the bench with a bench supply got me -130 dB second and -145 dB for the rest at 997 Hz (pretty much the limits of the Shibasoku). The power consumption is very low. I need to clean up the test setup before I can explore further. These are similar to what Victor measured.

The picture below is the distortion spectrum. The first peak is the second harmonic and the rest of the harmonics follow. The top line of the display is -80 dB and the vertical is 10 dB/div.
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File Type: jpg Victor-distortion.jpg (785.2 KB, 652 views)
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Old 15th August 2012, 10:35 AM   #223
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Uh oh, pulled the trigger on the 10k version too.

Thanks 1audio for confirmation of performance, and Victor for making the oscillators!

Yay yay yay, i've got myself some real analog test set.


Now i need to make some clock phase noise rig, and i'm done.
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Old 15th August 2012, 01:57 PM   #224
TheGimp is offline TheGimp  United States
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Thanks for the test results 1audio.

I previously ordered the 1K (due day before yesterday through next Tuesday) and just ordered the 10K as well. 0.025% from my Heath-kit just isn't cutting it.

Last edited by TheGimp; 15th August 2012 at 02:06 PM.
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Old 16th August 2012, 12:32 AM   #225
dimitri is offline dimitri  United States
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Demian, what was the load? Thx
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Old 16th August 2012, 04:07 AM   #226
dimitri is offline dimitri  United States
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Quote:
Here is the unfinished design for the fast settling state variable oscillator. It borrows the additional peak detecting ideas from Cordell's oscillator, adding more and uses a trick I have used making an LM339 work as a peak detector.
You may have a look here as well
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Old 16th August 2012, 04:07 AM   #227
davada is offline davada  Canada
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Demian what was the output level?

David.
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Old 16th August 2012, 06:13 AM   #228
1audio is offline 1audio  United States
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I'll try to get more data on the oscillator. The output is approx 2.7V full up. It has been stable for voltage (+/- .01dB) and frequency (995 Hz) for a day. I have been running it essentially unloaded. The pot and connector aren't even soldered in yet. The bulk of the measured distortion is second at -130dB++. This is good enough to test the limits of any ADC chip made today.

I'll get to the HF modules when I get to the chassis assembly phase in a week or two.
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Old 16th August 2012, 06:15 AM   #229
1audio is offline 1audio  United States
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Quote:
Originally Posted by dimitri View Post
You may have a look here as well
Its quite interesting. We are headed to the same goal. His implementation uses a few more parts to get to the same place.
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Old 16th August 2012, 01:36 PM   #230
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My 1kHz oscillator from Victor came in today. So far, I've only had time to power it up and check it on Visual Analyser via the Sound Blaster card on my workshop desk computer. Came in at 0.002%, but I'd be confident that that is the soundcard talking. So now I need one of Dick's active twin-tee filters to give the soundcard a sporting chance. Or a much better soundcard. Or both. Sigh....

Anyone planning to lay out the twin-tee filter? I'd hate to do that myself only to find out 237 other people have done it before me. And all of them better than mine.

Terry
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